1. Field of Invention
The present invention relates to a negative planographic printing plate precursor for infrared exposure having a photopolymerizable image recording layer which can be cured by infrared exposure.
2. Description of the Related Art
Conventionally, various systems have been developed for direct plate making from digital data of a computer. For example, since photopolymerization system image recording materials that are exposed using lasers, which emit blue or green visible light, are sensitive to an argon laser and the like, and make possible direct plate-making utilizing a photopolymerization initiating system with high sensitivity, such recording materials are being paid attention as recording layers for planographic printing plate which can attain high printing endurance due to a toughness of a coated film cured by photopolymerization.
For example, as a laser printing plate utilizing a photopolymerization initiating system, which is sensitive to visible lasers, such as argon lasers and the like, there is used a laser printing plate obtained by providing a photopolymerizable composition layer comprising a compound containing an addition polymerizable ethylenic double bond and a photopolymerization initiator, and optionally comprising, an organic polymer binder, a photopolymerization inhibitor and the like on an aluminium plate, which acts as a support, and providing on the photopolymerizable composition layer an oxygen intercepting layer, which inhibits polymerization. These photopolymerizable planographic printing plates provide an image by exposing a desired image to polymerize-cure an exposed portion, and removing (developing) an unexposed portion with an aqueous alkali solution.
Recently, development of lasers has been remarkable, and high output and compact solid lasers and semiconductor lasers, which radiate an infrared-ray having a wavelength of 760 nm to 1200 nm, in particular, are easily available. These lasers are very useful as a recording light source when direct plate-making from digital data, from a computer or the like. Therefore, in addition to the above-mentioned numerous and useful photosensitive recording materials, which are sensitive to a visible light region of 760 nm or shorter, materials on which recording can be performed with these infrared lasers are being developed.
As a material which is selectively sensitive to infrared light, positive image recording materials and negative image recording materials are known. A positive image recording material that utilizes a phase change of a novolak resin is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 9-43847. However, such positive image recording material has poor scarring (scratching) resistance, and there is a problem regarding handling properties thereof. On the other hand, as a negative image recording material which is excellent in scarring resistance, a material requiring no pre-heating is disclosed in JP-A Nos. 6-1088, 9-43845 and the like. However, there is a problem that such materials are inferior in image quality, in particular, in dot-reproducing properties.
In addition to make these planographic printing plate precursors, there are cases of using an image forming apparatus for supplying a plate material, and continuously performing imagewise exposure and development processing on-line, and cases of performing image formations successively off-line using an exposing device for continuously performing imagewise exposure to a plurality of planographic printing plate precursors and a developing device for developing the exposed plate material. In particular, in the latter, there is a problem that a time elapses after exposure by plate-making, thereby, a variation is generated in the sensitivity, and an image as designed can not be obtained.